A variety of architectural structures are known in the art, such as wooden structure, reinforced concrete structure, steel structure and so forth. As a kind of such an architectural structure, a masonry structure is known, in which walls and so forth are constructed by laying or stacking masonry units such as bricks or concrete blocks.
Bricks produced by baking a quantity of brick clay at a high temperature are highly evaluated by their architectural design effects or aesthetic effects resulting from their textures, stately appearances, feelings, colors and so forth. The bricks also exhibit their excellent physical performance with respect to durability, sound insulation effect, fire resistance efficiency, heat accumulation effect and so forth. Therefore, the bricks have been popularly used worldwide for a long time and widely employed as materials for architectural wall structures. Further, precast concrete products applicable to a masonry method, such as concrete blocks, exhibit relatively excellent performance with respect to economical efficiency, workability, durability, fire resistance efficiency and so forth. In recent years, designs for improving their architectural design effectiveness and reliability are appropriately employed, and therefore, the precast concrete products are widely and practically used for construction of walls.
In general, the masonry units, such as bricks, concrete blocks or the like, are laid by applying fresh mortar to the laying face. Accuracy of masonry, such as correctness to relative positions, intervals, levels and so forth, are adjusted timely during the masonry process. This kind of conventional masonry structure falls under a wet type of construction method.
On the other hand, the present inventor has proposed DUP (Distributed and Unbonded Prestress) Construction Method as a dry type of bricklaying construction method. According to this construction method, bricks are stacked in a multi-layered condition while pre-stress is introduced into the bricks by mechanical tightening force of metallic bolts, whereby a wall and the like having an earthquake resistant bricklaying structure can be constructed (Japanese patent applications Nos. 4-51893, 5-91674, 6-20659, 7-172603 and 8-43014).
The present inventor still continues the study for practical application of the DUP Construction Method. For example, in Japanese patent application No. 2000-270219 (Japanese patent laid-open publication No. 2002-81152), the present inventor has proposed the method in which a bolt hole and a large diameter hollow section are formed in position of a brick, whereby various intricate parts of wall structures can be constructed by the bricks having a common configuration and dimension. The present inventor has also proposed a Grid Method for enabling methodical and prompt design of distribution of the constituents used for the DUP Construction Method, in PCT international application No. PCT/JP03/09730. Further, the present inventor has proposed a double wall type of wall structure in which a brick wall built by the DUP Construction Method and an inner wall built by a dry type of construction method are connected for transmission of stress with each other by a shear reinforcement member.
Such a bricklaying method is a dry construction type of masonry method in which the bricks are integrally assembled by mechanical tightening force of nuts and bolts. This method has achieved its intended purpose, such as considerable reduction in construction time, compared with a conventional wet type of bricklaying construction method. However, according to this method, the walls, columns and so forth are built by fastening the bricks with the nuts and bolts, and therefore, adjustment of accuracy of masonry by fresh mortar can not be carried out. Thus, highly accurate dimensions of the bricks themselves are required. For instance, the vertically adjacent bricks are laid while the interlayer metal plate is interposed between the upper and lower bricks. Therefore, the upper and lower faces of the bricks in contact with the metal plate should be flat, smooth and horizontal with high accuracy. The height of each of the bricks should be dimensionally highly accurate as well. At present, the standard deviation of the accuracy with respect to the upper and lower faces of the brick (the target value as to the accuracy of the height of the brick) is set to be 0.118 mm, and the standard deviation of the accuracy with respect to the end faces of the brick (the target value as to the accuracy of the length of the brick) is set to be 0.142 mm.
Under such circumstances, the lying faces (the upper and lower faces) of the brick for the DUP Construction Method is ground in the production process, whereby horizontality, flatness and dimensional accuracy can be attained. If desired, the end face or both end faces of the brick are also ground in the production process for verticality, flatness and dimensional accuracy.
However, the steps for grinding the bricks after baking cause losses of water and energy for grinding, and the steps for grinding the bricks also result in losses of productivity and inexpensiveness of the bricks since the steps complicate the production process, waste time, cause addition of work or steps, increase production costs including labor costs, and create a shavings disposal problem and so forth. Thus, it is necessary to ensure high dimensional accuracy, flatness and horizontality (or verticality) of the lying faces (and the end faces) of the brick without the aforementioned grinding steps, thereby improving the productivity and inexpensiveness.
Further, each of the bricks for the DUP Construction Method is provided with through-holes having large and small diameters for accommodating a nut and a bolt respectively. Therefore, it is necessary to precisely bore the baked bricks in order to make two kinds of through-holes with different diameters. However, such boring steps for making these holes also cause losses of productivity and inexpensiveness of the bricks. If such through-holes can be formed on the brick by a relatively simplified step, productivity and inexpensiveness of the bricks would be able to be further improved.
Such problems are not limited to the bricks for the DUP Construction Method, but those problems would be also recognized similarly with respect to concrete blocks laid in accordance with the DUP Construction Method or a similar dry type of construction method.
The object of the present invention is to provide a method for forming a masonry unit used for a dry type of construction method utilizing mechanical tightening force of nuts and bolts, which can ensure high dimensional accuracy of each of the masonry units and promote efficiency of the production process of the masonry units, thereby improving productivity of the masonry units.
Particularly, the present invention is directed toward promotion of efficiency of production process of bricks used for the DUP Construction Method and improvement of productivity of these bricks.